Pimobendan, (4,5-dihydro-6-[2-(4-methoxyphenyl)-1H-benzimidazol-5-yl]-5-methyl-3(2H)-pyridazone) is disclosed in U.S. Pat. No. 4,361,563, herein incorporated by reference in its entirety. Pimobendan is a cardiotonic, hypotensive and anti-thrombotic. Said substance is useful in the treatment of congestive heart failure.
Pimobendan hardly dissolves in water. The resorption of pimobendan when administered orally is prone to considerable inter- and intra-individual fluctuations if the active substance is incorporated in known or conventional pharmaceutical forms for oral administration. The reason for this is that pimobendan is characterized by a low solubility in aqueous media and a very highly pH-dependent solubility. To overcome this, hard gelatine capsules were used containing pimobendan formulated with citric acid, in particular at a weight ratio of pimobendan to citric acid of between 1:10 and 1:20 (U.S. Pat. No. 5,364,646, herein incorporated by reference in its entirety). However, the high quantity of citric acid and the acidic taste of citric acid is not readily accepted by most animals—thus, such capsules have to be force-fed to the animals or mixed with food prior to application.
The problem underlying the present invention was to provide a pimobendan solid formulation readily acceptable by mammalian subjects, especially small animals.